Power over Ethernet (PoE) refers to delivery of power from power sourcing equipment (PSE) to powered devices (PDs) through Ethernet cabling. IEEE 802.3af is a standard which provides specific implementation details for such power delivery (e.g., see IEEE Std 802.3af-2003).
Examples of PSE include network switches, routers, hubs and midspans. Examples of PDs include wireless access points, IP phones, and IP cameras.
In general, the PSE carries out a discovery process through each network port to determine whether there is a remote device connected to that network port. If a remote device is connected to that network port, the PSE determines whether the PSE should deliver inline power to the remote device through that network port as part of the discovery routine. If the PSE decides to purposefully deliver inline power to the remote device, an inline power controller of the PSE turns on inline power to the network port by delivering an inline power signal from a power supply of the PSE to the network port. After the inline power controller turns on inline power to the network port, the inline power controller monitors an electrical characteristic at the network port to confirm the presence of an inline power signal, and reports an error if no inline power signal is detected while inline power is turned on.